Colorants are important components of food. Color affects consumer perception of food quality. Synthetic colorants are often used to impart color. Strict regulatory requirements make it difficult to obtain approval for new synthetic colorants. There is an unfilled need for a greater number of natural foods that incorporate natural colorants. A major obstacle is that many natural colorants are insoluble in water. Examples of water-insoluble, nonpolar natural colorants include the carotenoids and xanthophylls; many of these compounds are also believed to have beneficial health effects. The use of natural pigments has generally been restricted to hydrophobic environments. Water-based products have primarily used synthetic water-soluble colorants. Perceived health issues associated with synthetic colorants have triggered colorants. Perceived health issues associated with synthetic colorants have triggered an increased interest in natural colorants (pigments) suitable for use in foods. Prior approaches to incorporating lipophilic natural molecules in water-dispersible systems have included vehicles such as liposomes, vesicles, microparticles, and emulsions.
Many natural colorants, such as beta-carotene and curcumin, have not been well-suited for use in water-based food systems. Their low water solubility leads to non-uniform color distribution in the food, which is generally unacceptable to consumers. Many are also subject to oxidative degradation.
In the food industry, carotenoid colorants have primarily been used in hydrophobic environments. They have also been used in a limited number of emulsions and protein complexes in water-based foods. Carotenoids are widely distributed in nature. Natural annual production has been estimated at ˜108 ton/year of carotenoids, with a high percentage of that total from marine algae and green leaves. Other sources include peppers, saffron, red palm oil, and turmeric. Carotenoids are often found in free form in leaves, and esterified in other tissues. Carotenoids that have been approved by FDA for use as color additives include bixin and norbixin from annatto seeds, capsanthin and capsorubin from paprika extracts, and β-carotene from micro-algae or synthetic sources.
The European Union allows chlorophylls to be used as colorants. Chlorophyll, the compound primarily responsible for photosynthesis, is found in green plants, green algae, and cyanobacteria. Chlorophyll is a cyclic tetrapyrrole, with a magnesium atom coordinated in the center. Chlorophyll is typically is extracted with organic solvents. The thermal lability of the coordinated magnesium affects color stability, limiting chlorophyll's use as a colorant. Copper chlorophyllins, formed by chlorophyll saponification, are more stable and more water-soluble; copper is not as easily displaced as magnesium. Copper chlorophyllins are approved for use as colorants in the United States. They are typically prepared as a sodium or potassium salt, and tend to precipitate at low pH.
Curcumin is extracted from the rhizome of turmeric plant. It is yellow, soluble in nonpolar solvents, but almost insoluble in water at pH below 7. In alkaline pH the yellow color shifts to red and brown-red. Curcumin color is affected by light, temperature, oxygen, and the presence of metal ions, particularly when not protected by a lipophilic environment, for example when stored as a dry powder. Food-grade polysorbate 80 has been used as a surfactant or emulsifier for curcumin in water-based food products. Curcumin is less expensive than lutein, with similar greenish-yellow shades, but is more susceptible to photo-bleaching.
Anthocyanins are glycosides of anthocyanidins and sugars. Anthocyanins are water-soluble when a net charge is present. The most abundant natural source for anthocyanins is grape pomace, a byproduct of wine production. They have a range of colors, with higher levels of hydroxyl groups giving a more bluish color, and higher levels of methoxy a more reddish color. Likewise, color is affected by pH, typically ranging from purple-red at pH 3, to nearly colorless at pH 5, to blue or even green at a neutral or alkaline pH.
Emulsions have sometimes been used to make water soluble systems from lipophilic natural pigments. Surfactants (such as those in the polysorbitol family) are used to incorporate an oily natural pigment into micelles. They sometimes include stabilizing agents (e.g. antioxidants, antifoaming agents). However, such emulsions tend to be subject to phase separation.
There is an unfilled need for improved techniques to disperse lipophilic natural pigments and other nonpolar compounds in water, in a manner that provides good stability against oxidative degradation and photodegradation, and that is subject to minimal if any phase separation of the lipophilic compound from the water soluble matrix, over a reasonable range of pH and temperature.
A. Downham et al., “Colouring our foods in the last and next millennium,” International Journal of Food Science and Technology, vol. 35, pp. 5-22 (2000) is a recent review article, describing the history of food coloring, and the status of available colorants.
U. Klinkesorn et al., “Encapsulation of emulsified tuna oil in two-layered interfacial membranes prepared using electrostatic layer-by-layer deposition,” Food Hydrocolloids, vol. 19, pp. 1044-1053 (2005) discloses tuna oil-in-water emulsions stabilized with lecithin-chitosan membranes prepared as layer-by-layer electrostatic deposition. The initial tuna oil-in-water emulsion was prepared by placing tuna oil directly in a high-speed blender with an aqueous, buffered solution of lecithin; followed by passage through a high-pressure valve homogenizer. Particle diameters were reported at least as small as 260±10 nm.
T. Aoki et al., “Influence of environmental stresses on stability of 0/W emulsions containing droplets stabilized by multilayered membranes produced by a layer-by-layer electrostatic deposition technique, Food Hydrocolloids, vol. 19, pp. 209-220 (2005) discloses corn oil-in-water emulsions stabilized with sodium dodecyl sulfate-chitosan-pectin membranes prepared as layer-by-layer electrostatic deposition. The initial corn oil-in-water emulsion was prepared by corn oil directly in a high-speed blender with an aqueous, buffered solution of sodium dodecyl sulfate; followed by passage through a high-pressure valve homogenizer. Particle diameters were reported at least as small as 270±30 nm.
See also published U.S. patent applications 2005/0202149, 2007/0104849, 2007/0104866, and 2008/0044543.
U.S. Pat. No. 6,635,293 discloses an emulsion in which the aqueous phase contained an emulsifier, such as a sucrose fatty acid ester or a polyglycol ester, and an antifoaming agent. Carotenoids were mixed into the aqueous phase to form a stable emulsion. It was said that no elevated temperatures, high-shear mixing, or organic solvents were required to form the product, except that some ethanol might be added to reduce viscosity. The emulsion was a viscous liquid that could be used directly as an emulsion, or converted to freeze-dried form.
Other formulations have been based on colloids such as gelatins, including pork, cow, and fish gelatins. For example, U.S. Pat. No. 5,478,569 describes water-dispersible preparations of fat-soluble compounds, such as beta carotene, using fish gelatin as a hydrocolloid.
U.S. Pat. No. 6,007,856 describes oil-in-water dispersions of beta-carotene and other carotenoids that were said to be stable against oxidation. The oil-in-water dispersions are prepared from a water-dispersible beadlet containing a colloidal carotenoid, where the carotenoid is released from the beadlet and is in intimate contact with sufficient oil phase such that the carotenoid is stabilized against oxidation in the presence of the water phase. The beadlet is formed by dissolving the carotenoid in a water-miscible organic solvent (or dissolved in oil with heating), mixed with an aqueous solution of a swellable colloid (typically gelatin), precipitated in a colloidally dispersed form and then dried to form a colloidal dispersion or beadlet.
U.S. Pat. No. 6,444,227 discloses a process for preparing beadlets containing fat-soluble substances by forming an aqueous emulsion of a fat soluble substance, a gelatin, and a reducing agent; optionally adding a crosslinking enzyme; converting the emulsion into a dry powder; and crosslinking the gelatin matrix in the coated particles by exposing the coated particles to radiation or, if a crosslinking enzyme is present, by incubating the coated particles.
U.S. Pat. No. 6,406,735 discloses a process for making a pulverous preparation having a finely divided carotenoid, retinoid or natural colorant, which process comprises the steps of: a) forming a suspension of the active ingredient in a water-immiscible organic solvent; b) feeding the suspension to a heat exchanger; c) heating the suspension to 100-250° C., with a residence time in the heat exchanger less than 5 sec to provide a solution; d) rapidly mixing the solution of step c) with an aqueous solution of a swellable colloid so that the resulting mixture has a temperature 20-100° C.; e) removing the organic solvent; and f) converting the dispersion of step e) into a pulverous preparation.
U.S. Pat. No. 6,190,686 discloses water-dispersible compositions containing a hydrophobic pigment such as a carotenoid, curcumin, porphyrin pigment, or vegetable carbon. The pigments were dispersed in the aqueous phase, without a surfactant, using a hydrocolloid such as gelatin, milk protein, xanthan gum, agar, alginate, carrageenan, pectin, starch derivatives, dextran, or carboxymethyl cellulose.
U.S. Pat. No. 6,500,473 discloses the use of pectin to entrap natural pigments. Pectin having a high degree of acetylation was reported to protect natural pigments against degradation. Examples of natural pectins with a high degree of acetylation include beet, chicory, and Jerusalem artichoke.
U.S. Pat. No. 6,663,900 discloses a method of forming carotenoid microcapsules with a mixture of hydrocolloids. Crystalline carotenoid was processed in a fluidized bed coating machine, with a protective coating applied such as a sugar or sorbitol, a starch or maltodextrin, and optionally a coating protein such as gelatin.
U.S. Pat. No. 4,999,205 discloses a method of forming a complex between the natural colorant curcumin and a water-soluble polysaccharide or protein (e.g., gelatin) by reacting an aqueous alkaline solution of curcumin with the substrate in water, followed by neutralization to complex the curcumin to the substrate.
See also the following work by us and our colleagues: I. Zigoneanu et al., “Tocopherol encapsulated PLGA nanoparticles: Synthesis, Characterization and Stability,” Nanotechnology, vol. 19, p. 105606 (2008); G. Ganea et al., “Use of Experimental Design and Multivariate Analysis for Optimization of Poly (D,L-lactide-co-glycolide) (PLGA) Nanoparticle Synthesis Using Molecular Micelles,” J. Nanoscience and Nanotechnology (in press 2008); C. Astete et al., “Size Control of Poly(D,L-Lactide-co-Glycolide) and Poly(D,L-Lactide-co-Glycolide)-Magnetite Nanoparticles Synthesized by Emulsion Evaporation Technique,” J. Colloids and Surfaces A, vol. 299, pp. 209-216 (2007); C. Astete at al., “Synthesis and Characterization of PLGA nanoparticles: A review,” J. Biomaterial Science, Polymer Edition, vol. 17, pp. 247-289 (2006); and C. Sabliov et al., “Encapsulation and controlled release of antioxidants and vitamins via polymeric nanoparticles,” Chapter 17 in N. Garti (Ed.), Controlled Release Technologies for Targeted Nutrition (2008, in press).
There is an unfilled need for improved systems to solubilize lipophilic compounds, such as natural colorants, in water—systems that are stable (with minimum phase separation, precipitation, and oxidation), that employ natural products, that impart an uniform color or other uniformly dispersed properties in water, that are not overly sensitive to changes in temperature and other parameters, that are reproducible (batch by batch), scalable, and inexpensive.